Wafer-edge polishing system

ABSTRACT

A wafer-edge polishing device includes a buff member for polishing a semiconductor wafer, and a dresser for dressing the buff member, wherein the dresser opposes the buff member with an intervention of the semiconductor wafer. A wafer mount mounting thereon the semiconductor wafer and the dresser are respectively movable toward and from the buff member. The contact pressure between the wafer and the buff member as well as between the buff member and the dresser is fixed. The dresser performs in-situ dressing concurrently with polishing of the wafer by the buff member.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a wafer-edge polishing system and, moreparticularly, to the improvement of a wafer-edge polishing system forpolishing the edge portion of a wafer.

(b) Description of the Related Art

Semiconductor devices are manufactured by using a wafer such as asingle-crystal silicon wafer or compound semiconductor wafer, on whichoxide films, nitride films, carbide films, polycrystalline films,metallic films etc. are formed by sputtering technique, CVD techniqueand the like. The materials configuring those films may be deposited onthe edge of the semiconductor wafer and the vicinity thereof. Thematerials or films deposited on the edge portion of the wafer areunnecessary and often peeled off from the edge portion of the waferduring transportation of the wafer between different systems, such asbetween a cleaning system and a deposition system. If the depositedmaterials are peeled off from the wafer, the deposited materials may bea crucial contamination source against the product semiconductordevices. Thus, deposited materials should be removed using a wafer-edgepolishing system at any time if desired.

The wafer-edge polishing system includes a cylindrical buff unit ontowhich a buff member such as made of polyurethane foam or rigidpolyurethane resin is attached. Patent Publication JP-1995-40214Adescribes a wafer-edge polishing system, which is shown in FIG. 5. Thewafer-edge polishing system may be referred to merely as “polishingsystem” hereinafter.

In FIG. 5, the polishing system includes a cylindrical buff member 31which is rotatable with respect to the central axis 31 a thereof. Aslurry supply nozzle not shown is provided in the vicinity of the buffmember 31. A semiconductor wafer 40 is pressed against the cylindricalsurface of the buff member 31 at the edge of the semiconductor wafer 40.The semiconductor wafer 40 is slanted upward and downward, with the edgeof the semiconductor wafer 40 being fixed at the contact point of thecylindrical surface of the buff member 31, for polishing the entire edgeportion of the semiconductor wafer 40.

Patent publication as described above also shows another buff member,which is shown in FIG. 6. FIG. 7 shows the enlarged sectional view ofthe vicinity of the contact portion of the buff member 32 shown in FIG.6. The buff member 32 is rotated with respect to the central axis 32 athereof, and a slurry supply nozzle 34 supplies a slurry or polishingagent onto the vicinity of a groove 32 b configuring the contact portionof the buff member 32. The groove 32 b has a shape fitted to the edgeportion of the semiconductor wafer 40, thereby allowing thesemiconductor wafer 40 not to be slanted during the polishing.

The slurry or polishing agent generally includes minute silica particlesdispersed in an alkali or acidic liquid. The buff member configured bypolyurethane foam or polyurethane resin has a large number of minutecells (blowholes) on and inside the buff member. The minute cells assistthe buff unit to retain thereon the slurry, thereby improving thepolishing efficiency of the buff member.

It is noted that polished particles peeled off from the wafer orcontaminated slurry including the polished particles may enter theminute cells on the buff unit after an iterated polishing treatment,thereby clogging the minute cells. The clogging of the minute cellsprevents new slurry from entering the minute cells to lower thepolishing efficiency of the buff member. Thus, the buff unit should bereplaced by a new buff unit having minute cells not clogged by thepolished particles or contaminated slurry, to thereby improve thepolishing efficiency. The replacement of the buff unit reduces thethrough-put of the polishing treatment however.

SUMMARY OF THE INVENTION

In view of the above problems in the conventional techniques, it is anobject of the present invention to provide a wafer-edge polishing systemwhich is capable of improving the polishing efficiency, by reducing thefrequency of replacement of the buff unit in the polishing device toimprove the through-put of manufacturing semiconductor devices andreduce the cost for the buff unit.

The present invention provides a wafer-edge polishing system including:a wafer mount for mounting thereon a wafer; a polishing device movabletoward and from the wafer mount and having a buff member for polishingan edge portion of the wafer mounted on the wafer mount; a dressermovable toward and from the polishing device for dressing the buffmember of the polishing device.

In accordance with the wafer-edge polishing system of the presentinvention, the buff member having thereon polished particles orcontaminated slurry can be dressed by the dresser without replacement ofthe buff unit within the polishing system, thereby reducing thefrequency of the replacement of the buff unit, improving the polishingefficiency of the polishing system and improving the through-put ofmanufacturing the semiconductor devices.

The above and other objects, features and advantages of the presentinvention will be more apparent from the following description,referring to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of a polishing system according to anembodiment of the present invention.

FIG. 2 is a side view of the polishing system of FIG. 1.

FIG. 3 is a side view of the buff unit in the polishing system shown inFIG. 1.

FIG. 4 is a perspective view showing the buff unit of FIG. 3 beforebeing fixed onto the base pole.

FIG. 5 is a perspective view of a conventional polishing system.

FIG. 6 is a perspective view of another conventional polishing system.

FIG. 7 is an enlarged sectional view of a portion of the anotherconventional polishing system.

PREFERRED EMBODIMENT OF THE INVENTION

Now, the present invention is more specifically described with referenceto accompanying drawings, wherein similar constituent elements aredesignated by similar or related reference numerals.

FIG. 1 shows a polishing system according to an embodiment of thepresent invention in a top plan view thereof, and FIG. 2 shows thepolishing system in a side view thereof. The polishing system, generallydesignated by numeral 100, includes a wafer mount 15 for mountingthereon a semiconductor wafer 40, a pair of buff units 11 a, 11 b eachhaving a buff member 18 for polishing the edge portion of thesemiconductor wafer 40, a dresser 12 for dressing the buff members 18 ofthe buff units 11 a, 11 b, a pair of slurry supply nozzles 13 a, 13 bfor supplying a slurry to the contact portion between the edge of thesemiconductor wafer 40 and the buff members 18, and a pair of waternozzles 14 a, 14 b for supplying pure water to the contact portionbetween the buff members 18 and the dresser 12.

The buff members 18 are rotatably fixed onto the top of base poles 16disposed for the buff units 11 a, 11 b. The dresser 12 is also rotatablyfixed onto the top of a base pole 17 disposed for the dresser 12. Asshown in FIG. 2, the semiconductor wafer 40 rotates in the clockwisedirection, the buff units 11 a, 11 b rotate in the clockwise direction,and the dresser 12 rotates in the counter-clockwise direction.

In the polishing system 100, the edge portion of the semiconductor wafer40 mounted on the wafer mount 15 is polished by the buff members 18,which are in turn dressed by the dresser 12 at the same time, wherebythe dresser 12 assists the cylindrical buff members 18 to polish theedge portion of the semiconductor wafer 40.

The semiconductor wafer 40 is fixed onto the wafer mount 15 by usingvacuum contact. The wafer mount 15 is associated with adisplacement/rotation mechanism including an air cylinder, a steppingmotor and a variable-speed motor, which are not specifically shown inthe figure. Thus, the wafer mount 15 is movable in the X- andZ-directions shown in FIG. 2, and is rotatable with respect to thecentral axis thereof. The air cylinder is provided with a pressuresensor for detecting the internal pressure, based on which the contactpressure between the semiconductor wafer 40 and the buff members 18 iscontrolled at a fixed pressure.

The dresser 12 is made of a cylindrical stainless steel plate, ontowhich minute synthetic diamond particles are fixed by anelectro-depositing technique. The dresser 12 is subjected to shaping forfixing the same onto the base pole 17 for the dresser 12. The base pole17 for the dresser 12 is also associated with displacement/rotationmechanism including an air cylinder, a stepping motor and avariable-speed motor, similarly to the wafer mount 15, which are notspecifically shown in the drawings. Thus, the base pole 17 for thedresser 12 is movable in X- and Z-directions and rotatable with respectto the central axis thereof. The air cylinder is provided with apressure sensor for detecting the internal pressure, based on which thecontact pressure between the dresser 12 and the buff members 18 iscontrolled at a fixed pressure.

The slurry supply nozzles 13 a, 13 b are disposed at the location andangle such that the slurry used as the polishing agent is directlysupplied onto the contact portion between the wafer 40 and the buffmembers 18. Similarly, the water nozzle 14 a, 14 b are disposed at thelocation and angle such that the pure water is directly supplied ontothe contact portion between the dresser 12 and the buff members 18.

Since the buff units 11 a, 11 b have similar structures, materials anddimensions, the configuration and function of buff unit 11 b alone willbe described hereinafter with reference to FIG. 3. FIG. 3 is a side viewof buff unit 11 b. Buff unit 11 b includes the buff member 18 having asubstantially cylindrical shape, a strut 19 penetrating the buff member18 at the central bore thereof, an insertion member 21 formed at thebottom of the strut 19, and a boss 20 protruding radially outside theinsertion member 21.

The buff member 18 is of an axial symmetry. The buff member 18 is madeof polyurethane foam having a hollow cylindrical shape, and the outercylindrical surface of the buff member 18 has a depression at thecentral portion thereof as viewed in the axial direction. Thus, the buffmember 18 has a U-shaped sidewall, as viewed in the horizontaldirection. The U-shaped sidewall includes roughly a top flange-shapedportion, an upper curved portion 18 a of a truncated corn, a centraldepression, a lower curved portion 18 b of a truncated corn, and abottom flange-shaped portion. The buff member 18 may be made of rigidpolyurethane resin instead.

Polishing treatment of semiconductor wafers 40 abrades the surface ofthe buff member 18, thereby necessitating a regular replacement of thebuff unit 11 b as an expendable part. FIG. 4 is a perspective view ofbuff unit 11 b before being mounted on top of the base pole 16. The buffunit 11 b is fixed onto the base pole 16 by the steps of aligning theboss 20 with a slot 22 of the base pole 16, inserting the insertionmember 21 into a hole 23 of the base pole 16, and fixing buff unit 11 bon the base pole 16 by using thrust screws 24. Removal of buff unit 11 bis effected in the order reversed from the recited order.

Operation of the polishing system of FIG. 1 will be describedhereinafter with reference to FIGS. 1 to 3 in separate steps. In a firststep, a semiconductor wafer 40 is delivered from a wafer cassette etc.by a wafer transportation system onto top of the wafer mount 15. Thebottom surface of the semiconductor wafer 40 is absorbed by the top ofthe wafer mount 15 using vacuum contact, whereby the semiconductor wafer40 is fixed on the wafer mount 15. In a second step, the slurry supplynozzles 13 a, 13 b supply the slurry as a polishing agent in a specifiedamount, and the buff units 11 a, 11 b are rotated by the base poles 16at a specified rotational speed.

In a third step, the dresser 12 is rotated by the base pole 17 at aspecified rotational speed, and then moves in the X-direction to contactthe buff members 18 of the buff units 11 a, 11 b. The contact pressureof the dresser 12 with respect to the buff members 18 is controlled by apressure control mechanism including the air cylinder of the base pole17. In a fourth step, the semiconductor wafer 40 is rotated with respectto the central axis of the wafer mount 15 and moved in the X-directionto contact the buff members 18 of the buff units 11 a, 11 b at the edgeof the semiconductor wafer 40. The contact pressure of the edge of thesemiconductor wafer 40 with respect to the buff members 18 is controlledby the pressure control mechanism including the air cylinder of thewafer mount 15. Thus, the semiconductor wafer 40, buff units 11 a, 11 band dresser 12 are rotated by separate rotation mechanisms, and both thewafer 40 and dresser 12 are thrust or pressed against the buff members18 at a specified contact pressure.

In a fifth step, the semiconductor wafer 40 is moved in the X- andZ-directions while being rotated, with the edge of the wafer 40 beingmoved along and polished by the U-shaped sidewall of the buff members18. The top and bottom bevels of the edge of the wafer 40 are polishedby the curved portions 18 a, 18 b of the U-shaped sidewall of the buffmembers 18. The dresser 12 is also moved in the X- and Z-directionswhile being rotated, with the edge of the dresser 12 moving along andabrading the U-shaped sidewall of the buff members 18. Abrasion of thebuff members 18 by the dresser 12 allows the buff members 18 to expose anew surface thereof and removes the clogging of the minute cells by thepolished particles or contaminated slurry, whereby the new surface ofthe buff members 18 is exposed at any time.

The semiconductor wafer 40 and dresser 12 periodically move in theZ-direction during polishing and dressing, wherein the periodicalmovement of he semiconductor wafer 40 in the Z-direction has a periodsame as that of the periodical movement of the dresser 12 in theZ-direction. In addition, the periodical movement of the semiconductorwafer 40 is deviated by half the period in the phase from the phase ofthe periodical movement of the dresser 12. For example, when the wafer40 is located at the upper curved portion 18 a of the buff members 18,the dresser 12 is located at the lower curved portion 18 b of the buffmembers 18. On the other hand, when the wafer 40 is located at the lowercurved portion 18 b of the buff members 18, the dresser 12 is located atthe upper curved portion 18 a of the buff members 18.

Employment of such a locational relationship between the wafer 40 andthe dresser 12 prevents the wafer 40 and the dresser 12 from beinglocated at the same position of the buff members 18 as viewed in theZ-axis direction. This avoids the situation wherein the dresser 12removes the new slurry from the buff members 18 in a period before thebuff members 18 use the new slurry for polishing the wafer 40, the newslurry being supplied from the slurry supply nozzles 13 a, 13 b in thesame period. Thus, the new slurry stays at any time between the wafer 40and the buff members 18, thereby preventing reduction in the polishingefficiency.

After the edge of the semiconductor wafer 40 is polished, the polishingprocess advances to a sixth step, wherein the semiconductor wafer 40 istransferred by a wafer transportation system to a wafer cleaning system,wherein the remaining slurry is removed. Thereafter, the semiconductorwafer 40 is returned to the wafer cassette. A next semiconductor waferis then supplied to the wafer mount 15, and the water nozzles 14 a, 14 bsupply pure water to the contact portion between the buff members 18 andthe dresser 12, whereby the buff members 18 are dressed by the dresser12 for cleaning of the surface. Those first through sixth steps areiterated for polishing the edge portion of a number of semiconductorwafers 40.

In the present embodiment, the dresser is installed in the polishingsystem which polishes the edge of semiconductor wafers, whereby both thepolishing and dressing are performed in a single process. This preventsclogging of the minute cells on the surface of the buff members, theclogging being caused by the polished particles or contaminated slurryand causing reduction in the polishing efficiency. Thus, the presentembodiment achieves a higher polishing efficiency and thus a higherthrough-put in the polishing.

Removal of the clogging from minute cells on the surface of the buffmembers by the in-situ dressing eliminates necessity of the replacementof buff units caused by the clogging, thereby reducing the frequency ofthe replacement of the buff units. This improves the operation rate ofthe polishing system.

In the configuration of the present embodiment, dressing of the buffmembers gradually reduces the diameter of the buff members. However, thecontrol of the contact pressure between the semiconductor wafer and thebuff members as well as between the buff members and the dresser allowsa continuous operation of the polishing and dressing irrespective of thereduction in the diameter of the buff members.

In the configuration of the present embodiment, the in-situ dressingtreatment is used, wherein the dressing is concurrently performed withthe polishing. The in-situ dressing treatment allows a plurality ofsemiconductor wafers to be polished in a continuous processing withoutreplacement of buff units, thereby achieving a higher through-put in thepolishing. However, this is not essential to the present invention, andan ex-situ dressing may be performed in the present invention. In thiscase, a single ex-situ dressing may be inserted at the interval betweenpolishing of a wafer and polishing of another wafer, or betweenpolishing of a plurality of wafers and polishing of another plurality ofwafers.

Since the above embodiments are described only for examples, the presentinvention is not limited to the above embodiments and variousmodifications or alterations can be easily made therefrom by thoseskilled in the art without departing from the scope of the presentinvention. For example, the polishing system of the present inventionmay be used for polishing a wafer other than a semiconductor wafer. Theterm “wafer” as used herein means a relatively thin and flat object,such as a disk or disk-like plate.

1. A wafer-edge polishing system comprising: a wafer mount for mountingthereon a wafer; a polishing device movable toward and from said wafermount and having a buff member for polishing an edge portion of thewafer mounted on said wafer mount; a dresser movable toward and fromsaid polishing device for dressing said buff member of said polishingdevice.
 2. The wafer-edge polishing system according to claim 1, whereinsaid polishing by said polishing device and said dressing by saiddresser are performed concurrently.
 3. The wafer-edge polishing systemaccording to claim 1, wherein said polishing by said polishing deviceand said dressing by said dresser are performed alternately.
 4. Thewafer-edge polishing device according to claim 1, wherein said wafermount, said buff member and said dresser are capable of being rotatedwith respect to respective central axes thereof independently from oneanother.
 5. The wafer-edge polishing device according to claim 4,wherein said buff member has a cylindrical surface capable of being incontact with said wafer and said dresser, said wafer mount and saiddresser move periodically in a direction parallel to said central axesat least in a range wherein said wafer and said dresser are capable ofbeing in contact with said cylindrical surface, and periodical movementof said wafer mount has a period same as a period of periodical movementof said dresser and a phase opposite with respect to a phase of saidperiodical movement of said dresser.
 6. The wafer-edge polishing deviceaccording to claim 1, further comprising a pressure controller forcontrolling the contact pressure between the wafer and said buff memberand/or the contact pressure between said dresser and said buff member.